1. Field of the Invention
The present invention relates to a solid state image sensor and, more particularly, to a solid state image sensor and a method for fabricating the same which is adapted to simplify the process and enhance the morphology of the sensor.
2. Discussion of Related Art
With reference to the attached drawings, a conventional solid state image sensor and its fabricating method will be described below with respect to a method of forming a metal line between PDs (Photo-Diodes).
FIG. 1 is a cross-sectional view of a solid state image sensor fabricated according to prior art and FIGS. 2a-2e are cross-sectional views illustrating a method of fabricating the conventional solid state image sensor, wherein there are shown a pixel region, a contact forming region in a ferry region, and a pad forming region in the order from the left side of the figures.
Such a solid state image sensor, as shown in FIG. 1, has first, second and third transfer gates 12, 13 and 14 between the PDs of the pixel region and in the contact forming region of the ferry region.
An HLD (High-temperature and Low-pressure Dielectric) layer 15 is provided to surround the first, second and third transfer gates 12, 13 and 14. There are further formed a second aluminum film 21 approximately 4000 .ANG. thick as a light-shielding layer in the region exclusive of the photo-diodes, and a passivation layer 23 on the whole surface in the pixel region .
A contact hole is disposed between the HLD layer 15 and a smooth protective layer 16, exposing defined regions of the first, second and third transfer gates 12, 13 and 14 in the contact forming region. Further, a first aluminum film 17 is formed on the contact hole and smooth protective layer 16 and an insulating layer 19 consisting of PSiO is formed on the first aluminum film 17. On the insulating layer 19 is disposed a passivation layer 23.
On substrate 11 in the pad forming region are sequentially laminated HLD layer 15, smooth protective layer 16 and first aluminum film 17. The insulating layer 19 and passivation layer 23 are pad-open such that a defined portion of the first aluminum layer 17 is exposed.
FIGS. 2a-2e are cross-sectional views illustrating a method for fabricating such a conventional solid state image sensor.
As shown in FIG. 2a, a substrate 11 has first, second and third transfer gates 12, 13 and 14 laminated between PDs (Photo-Diodes) and in the ferry region, and an HLD layer 15 surrounding the first, second and third transfer gates 12, 13 and 14. A nitride layer is deposited on the substrate 11 and a part of the nitride layer disposed in the ferry region is then eliminated. After deposition of a smooth protective layer 16 on the substrate 11, a photo resist is deposited on the whole surface. Part of the photo resist in the contact forming region is then selectively patterned through an exposure and a development. Using the photo resist patterned as a mask, the smooth protective layer 16 and HLD layer 15 in the contact forming region are eliminated, exposing defined portions of the first, second and third transfer gates 12, 13 and 14. A first aluminum film 17 is deposited on the whole surface by a sputtering technique. Subsequently, a photo resist 18 is formed on the whole surface of the substrate 11 and selectively patterned through an exposure and a development to eliminate only the pixel region.
As shown in FIG. 2b, the photo resist 18 patterned is used as a mask in eliminating the first aluminum film 17 in the pixel region. An insulating layer 19 consisting of PSiO is deposited on the smooth protective layer 16 in the pixel region and on the first aluminum film 17 in the contact forming region and in the pad region.
As shown in FIG. 2c, a photo resist 20 is formed on the whole surface and selectively patterned through an exposure and a development such that only the photo resist 20 in the pixel region is eliminated. The photo resist 20 selectively patterned is used as a mask to eliminate the insulating layer 19 and smooth protective layer 16.
As shown in FIG. 2d, following removal of the photo resist 20, a second aluminum film 21 is formed on the whole surface of the substrate 11 by the sputtering technique. A photo resist 22 is formed on the second aluminum film 21 and selectively patterned through an exposure and a development, etching the upper portion of the photo-diode in the pixel region and the photo resist 22 in the ferry region.
As shown in FIG. 2e, the photo resist 22 patterned is used as a mask in performing an anisotropic etching of the upper portion of the photo-diode in the pixel region and the second aluminum film 21 in the ferry region. On the whole surface of the substrate 11 is deposited a passivation layer 23 consisting of PSiN. Next, the passivation layer 23 in the pas forming region and the insulating layer 19 consisting of PSiO are anisotropically etched to expose the first aluminum film 17.
However, such a solid state image sensor and method for fabricating the same involves a problem that the entire number of processes is increased with a consequence of reduction in the productivity because two time of deposition of the aluminum film is required in forming the light-shielding layer in the pixel region and the metal line in the contact forming region and the pad forming region of the ferry region.